In July 2011, U.S. President Barack Obama welcomed the birth of South Sudan, a nation that emerged free of its northern neighbor after decades of war and millions of lives lost and ruined. “This historic achievement is a tribute, above all, to the generations of southern Sudanese who struggled for this day,” said Obama in a statement then. The bitterness still felt by many in the new South Sudan toward the Sudanese leadership in Khartoum smoldered. After a swearing-in ceremony in Juba, the fledgling state’s capital, freshly-appointed South Sudanese President Salva Kiir declared: “We have been bombed, maimed, enslaved, and treated worse than a refugee in our own country. We have to forgive, although we will not forget.”

But two years on, there’s a lot more forgiving for South Sudanese to do—and this time the north is not to blame. The past two weeks have seen a shocking round of violence across the country as forces loyal to Kiir clamped down on rebel fighters associated with Kiir’s former Vice President, Riek Machar. According to the U.N., more than a thousand people were killed in a matter of days as armed groups on both sides reportedly targeted civilians for slaughter. Some 120,000 South Sudanese have been displaced by the mayhem. Mass graves were uncovered. Fears of an ethnically-charged civil war—Kiir hails from the Dinka tribe, the largest in a very diverse nation, and Machar from the Nuer tribe—have grown in a country that’s no stranger to the enmities of myriad factions and militias.

A ceasefire negotiated Friday at a meeting of East African leaders in Nairobi provides a reprieve, but not a lasting solution to the strife. The government of South Sudan’s official Twitter feed claimed on Dec. 27 that it had agreed “in principle” to a cessation of hostilities, but reports of clashes continued and parts of the country—including the main city in the oil-rich (and ironically-named) Unity state—remain under the control of rebel forces. Machar, speaking to the BBC on a satellite phone “from the bush,” was wary of the truce and demanded that 11 prominent prisoners currently detained by the government be released. The men in question are alleged, alongside Machar, to have participated in a failed coup against Kiir earlier this month—though the government’s version of events is disputed by its opponents. According to reports, the South Sudanese government has now agreed to free all but three of the imprisoned officials. They are members of the ruling Sudan People’s Liberation Movement (SPLA) party, a political institution that came into existence first as a guerrilla force combating Khartoum, but is riven by its own longstanding internal divisions that have flared into conflict in the past.

The U.N. is bolstering its peacekeeping forces in the country while aid organizations will attempt to rush relief to violence-hit areas. But even if the battles get subdued, the cracks within South Sudan will be hard to paper over. All new nations have their growing pains—just look at the dysfunctions still wracking East Timor and Kosovo. South Sudan, though, was dealt a particularly tough hand: crushing poverty, one of the world’s lowest literacy rates, woeful infrastructure and a glut of oil that breeds corruption among a coterie of ruling elite. Kiir has been accused of deploying a somewhat “authoritarian hand” in his two and a half years in power, which may have provoked Machar’s mutiny. Without mature state institutions to manage political divisions, the tensions exploded into armed conflict that took on an ethnic character and led to massacres of innocents.

The chaos now must be particularly disappointing to Washington, which has given over a billion dollars in aid to Juba since 2011 and played an instrumental role in negotiating the peace with Khartoum that led to South Sudan’s creation. Skirmishes with the north over the still-disputed border continue and almost led to open war in 2012, while various rebellions in both Sudans have threatened regional stability. But the current crisis is the most existential challenge yet. The international community has invested too much to let South Sudan collapse, but, perhaps for the first time, it is up to its own leaders—and not outside powers—to pull it away from the brink.